This invention relates to the transformation of the fluid movement (flow) energy and, in the most important example, to the usage of wind energy to provide the renewable source of mechanical or electrical power.
Wind turbines convert wind energy into electricity. The two main types of wind turbines include the horizontal-axis wind turbines and the vertical-axis wind turbines. The current models of practically used wind-driven engines fall in two main categories: propeller systems with horizontal axis of rotation also known as horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). The later have the advantage of more economic use of ground (or water) area, lower cost and easier maintenance. One advantage of VAWT systems is that the turbine doesn't need to be pointed into the wind. Another advantage of the VAWT arrangement is that the generator and/or gearbox can be placed at the bottom, near the ground, so the tower doesn't need to support it.
The two main types of vertical axis wind turbines include one type having rotating blades without lift generating surfaces and include the Darreius-Type having rotating blades with lift generating airfoils (VAWT). The HAWT typically has a rotor and blades with lifting surfaces mounted on a horizontal-axis and directed upwind atop a tower. Wind energy incident to the blades rotates the rotor, and a gearbox and other components are connected to the rotor communicate the rotation to an electric generator that converts the rotation to electrical energy. To be effective, the blades must be directed relative to the direction of the wind. Therefore, the HAWT typically has a yaw mechanism to allow the blades to rotate around the tower. Because the blades are upwind of the tower, they must be made of rigid, strong material so they cannot be bent back by the wind and hit the tower. Requiring more rigid materials, the blades are more expensive to manufacture and are heavy. In addition, the tower's yaw mechanism must be strong so it can determine the direction of the wind direction and orient the blades into the direction of the wind. Finally, the tower must also be strong so it can support the heavy rotor, gear-box, generator, and other equipment on top of the tower. Therefore, the tower requires more materials, is more expensive to build, and is heavy. Overall, the HAWT is a ‘rigid’ wind turbine, requires more materials, is heavy, and has a high center of gravity. In addition, it needs to be oriented to face the wind, and requires a firm foundation or platform. Therefore, it is very expensive to build a floating platform to support the HAWT, which is heavy, has a high center of gravity, and requires a very stable platform.
By contrast, the conventional VAWT uses a rotor that runs vertically from the ground and has curved blades connected at the rotor's ends. This vertical rotor sits on a bearing and gearbox component and drives an electric generator. Unlike the HAWT, the VAWT is omni-directional and does not need to be oriented into the wind. In addition, the VAWT has a low center of gravity with its heavy components such a gearbox, generator, braking and control system positioned near the ground. Therefore, the VAWT does not require an as rigid rotor as with the HAWT's tower to support these components. Example of VAWTs in the prior art can be found in the website of www.ecopowerusa.com. The HAWTs have been widely used in land-based windfarms around the world. HAWTs have also been used in offshore windfarms in Europe. A conventional offshore HAWT 30 has the conventional components of a rotor and blades supported horizontally on a vertical tower. These conventional components rest on a fixed support rigidly affixed to the sea floor. Examples of the offshore HAWT can be found in U.S. Patent Application Publication 2007/0040388, published February 2007, and PCT Published Application WO/03/004870, published Jan. 16, 2003. Another type of conventional offshore HAWT also has the conventional components of rotor, blades, and tower, but these components rest on a floating support that is rigidly affixed to the sea floor by cables. An example of this type of conventional HAWT can be found in PCT Application Publication 2005/021961, published Mar. 10, 2005.
United States Patent Application 2009/0072544 discloses an offshore wind turbine with a vertical-axis wind turbine (VAWT) mounted on a platform. The VAWT has a vertical rotor and curved blades coupled to a gearbox and an electric generator. The VAWT can fixedly extend from the platform or may be capable of reclining on the platform either manually or automatically. The platform can be composed of modular elements coupled together. Offshore, the platform can be semi-submersible with the VAWT extending out of the water and with a counterbalance extending below the platform. Alternatively, the platform can float on the water's surface and can have several arms that extend outwardly from the VAWT to increase the platform's footprint. To anchor the turbine offshore, anchoring systems can anchor the platform to the seabed while allowing the floating wind turbine to adjust passively or actively to changes in sea level due to tidal variations or storm swells.
As these prior art publications disclose many well-known implementation details concerning the design and operation of wind turbines generally, they are all incorporated herein by reference in their entireties.